Geographical and temporal patterns of green turtles along the Southwestern Atlantic coast

FALLABRINO A; ESTRADES A; GOMES DA SILVA BM; BAPTISTOTTE C; BEZERRA DP; ALBAREDA D; GUEBERT F; LOPEZ GG; DE CASTILHOS JC; WANDERLINDE J; MARCOVALDI MA; ESTIMA S; BARATA PCR; DOS SANTOS AS; SANTOS AJB; GIFFONI B; BELLINI C; MONTEIRO DS; LIMA EHS; VÉLEZ-RUBIO GM; STAHELIN GD; THOMÉ JCA; BARROS J; MELO MTD; NARO; GONZÁLEZ CARMAN V; BONDIOLI A; DA SILVA ACC; DOMIT C; BATISTA CMP; RIETH D; PAES E LIMA E; SALES G; BRUNO I; BECKER JH; ROSA L; MASCARENHAS R

Lima

Simposio; 36th Annual Symposium on Sea Turtle Biology and Conservation; 2016

Green turtles (Chelonia mydas) are commonly found along the eastern coast of South America. Here we use a large-scale data set (N = 20,938) to investigate the spatial and temporal distribution of green turtles recorded in Brazil, Uruguay and Argentina from June 2005 to May 2011 (six years of observations). The green turtle is currently classified as Vulnerable in Brazil, Vulnerable in Uruguay and Threatened in Argentina, and is globally listed as Endangered by the International Union for Conservation of Nature (IUCN).The turtles were recorded between latitudes 2.93 and 42.57 degrees South (from Ceará, northern Brazil to northern Patagonia, Argentina), a region comprising about 6,800 km of coastline. The records were obtained by sea turtle conservation organizations in the three countries during their regular activities, rather than through dedicated sampling. Turtles were observed either alive or dead in four different ways: (1) stranded on beaches; (2) floating along the coast; (3) incidentally captured in coastal fisheries; or (4) intentionally captured in coastal waters by sea turtle researchers. Only turtles for which the curved carapace length (CCL, from the anterior point at midline (nuchal scute) to the posterior tip of the supracaudal scutes) was measured were included in the analyses. As a way of avoiding sampling bias, some analyses were only carried out for turtles found stranded on beaches regularly monitored for strandings in the six years (N = 6,929). Here we present analyses of the CCL variation by latitude and time, of the relationship between CCL and sea surface temperature, seasonal patterns of green turtle occurrence, and other analyses. The CCL of sampled individuals was in the range of 8-130 cm. The estimated sea surface temperature at sampling was in the range of 8.74-30.50 °C. The most conspicuous pattern in the available data is a latitudinal variation in the CCL distribution, with a clear gradual narrowing of its spread from north to south: the quantiles 0.05 and 0.95 of the CCL are, respectively, 30.0 and 96.0 cm to the north of latitude 15° S (Bahia, Brazil) (N = 5,729), 30.5 and 55.0 cm between latitudes 15° S and 30° S (Rio Grande do Sul, Brazil) (N = 13,392), and 32.0 and 50.0 cm to the south of latitude 30° S (N = 1,817). Fifty-five very small turtles (CCL ≤ 20 cm) were found, of which 53 (96.4%) were to the north of latitude 15° S, and 400 turtles with CCL ≥ 90 cm were found, of which 373 (93.3%) were also to the north of latitude 15° S.This research advances the current understanding of green turtle population biology in the Southwestern Atlantic and provides a wider scientific basis for regional conservation of the species.